The present invention relates to a combustion seal ring having a layered composite powdered metal construction for use with a cylinder head gasket.
A cylinder head gasket bears a clamping load from a bolted connection of a cylinder head and an engine block and relies upon that load to provide a seal against the sealing elements of the gasket.
Several types of combustion seal rings are known. One type, known as a yieldable combustion seal ring, is essentially comprised of a wire having a generally circular cross-sectional area. A clamping force applied to such a ring is concentrated at the point of contact, deforming the ring's circumference to effectively seal out combustion gases. This type of seal ring, however, is subject to thermal crushing which results from plastic deformation which tends to occur under high temperature operation during the life of the ring.
To address the thermal crushing problem, a "thermal stop" combustion seal ring is sometimes used. This "thermal stop" seal ring has a generally rectangular cross-sectional area, which is more resistant to thermal crushing because of the increased surface area upon which a clamping load acts. One disadvantage of this particular type of ring, however, is that due to its large surface area and lack of point loading, it has very poor deformability.
To overcome disadvantages of the yieldable combustion seal ring and the "thermal stop" combustion seal ring, a combustion seal ring is known which has a central section of generally circular cross-section and a single tab section of generally rectangular cross-section extending radially outwardly away from the central section. It is also known to use a first metal for the central section and a second metal for the tab section.
This type of seal ring is still subject to numerous disadvantages. The use of two separate metals complicates manufacture. Such a ring also requires a compromise between a desired vertical compressive yield strength and a hoop yield strength. Hoop yield strength is measured tangentially to the ring's circumference and should be sufficiently high to withstand the internal cylinder pressures produced during engine operation. If a ring does not have adequate hoop strength, it will tend to expand allowing combustion gases to leak. At the same time, however, a low vertical yield strength is desirable to provide a deformable seal ring which completely seals against the leakage of combustion gases. Further, with such prior art seal rings stiffness may not be selectively varied along a selected axis to increase the flexibility of the ring. Additionally, the use of a single radially inwardly extending tab section may not provide sufficient hoop strength to resist gas blow out forces.